1) By default JMS does NOT share everything and therefore when you change a content in a website, it is not update into the other websites.
Only a limited number of extension can be shared.
www.jms2win.com/component/content/article/135
or click on the "help" button present in the "JMS tools" menu.
2) As by definition you have specific content, you can create a custom HTM for the header.
If in the header you have very limited of things, you can also use plugin like "Search/Replace" to change some keywords with real value.
www.jms2win.com/free-download/doc_downlo...rch--replace-utility
3) As all the website are independent and therefore also the article, you may perhaps need the "Article Sharing for JMS" that is used to read articles coming from any websites.
So you could read your "common or shared" articles from a unique place.
See the
www.jms2win.com/download?page=shop.produ...pl&product_id=34